挖掘性能瓶颈的利器-Btrace实例-check 程序中的线程数

Btrace无疑是性能调优的一个非常重要的工具，它可以做到代码无侵入性的挖掘性能的问题，它利用字节码级别的运行时动态植入来check性能问题，性能优化的第一步往往是找出性能的瓶颈，如下面的功能是check程序的运行的线程数：

 

 

/*
 * Copyright 2008-2010 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package example3;

import static com.sun.btrace.BTraceUtils.println;
import static com.sun.btrace.BTraceUtils.str;
import static com.sun.btrace.BTraceUtils.threadCount;

import java.util.concurrent.atomic.AtomicInteger;

import com.sun.btrace.BTraceUtils.Atomic;
import com.sun.btrace.BTraceUtils.Strings;
import com.sun.btrace.BTraceUtils.Threads;
import com.sun.btrace.annotations.BTrace;
import com.sun.btrace.annotations.Export;
import com.sun.btrace.annotations.OnMethod;
import com.sun.btrace.annotations.OnTimer;
import com.sun.btrace.annotations.Self;

/**
 * This sample creates a jvmstat counter and
 * increments it everytime Thread.start() is
 * called. This thread count may be accessed
 * from outside the process. The @Export annotated
 * fields are mapped to jvmstat counters. The counter
 * name is "btrace." + <className> + "." + <fieldName>
 */
@BTrace public class ThreadCounter {

    // create a jvmstat counter using @Export
    @Export private static AtomicInteger count=new AtomicInteger(0);

    @OnMethod(
        clazz="java.lang.Thread",
        method="start"
    )
    public static void onnewThread(@Self Thread t) {
        // updating counter is easy. Just assign to
        // the static field!
        println(Strings.strcat("starting ", Threads.name(t)));
        Atomic.addAndGet(count, 1);
    }

    @OnTimer(2000)
    public static void ontimer() {
        // we can access counter as "count" as well
        // as from jvmstat counter directly.
        println(Strings.strcat("total thread count:", str(threadCount())));
        println(Strings.strcat("start thread count:", str(count)));
    }
}